Printed circuit boards are widely used for mounting and interconnecting components in circuit assemblies. Such circuit boards are fabricated in many varieties, including single-sided boards, double-sided boards and multi-layer boards, and with conductors and connecting arrangements compatible with the number and spacing of terminals on the most complex electronic devices, such as integrated circuits embodying microprocessors, memory, digital controllers and the like.
To conserve space, it is often desirable to arrange printed circuit boards in a three-dimensional structure. This can be accomplished by plugging circuit boards into connectors mounted in a backplane, mounting circuit boards perpendicular or parallel to other boards and various other arrangements.
Mounting circuit boards parallel to each other can be a particularly effective way of achieving a three-dimensional structure, provided that the necessary connections can be made between adjacent boards. Various means are available for making such connections, for example, the interconnecting spacers described in the article entitled "A 3-D System for Interconnection Meets the Challenge of High Density Packaging" beginning on page 84 of the Apr., 1985 issue of Electronic Packaging and Production, stacking connectors made by suppliers such as Teledyne Kinetics, Solana Beach, Calif. and Cinch, Chicago, Ill. and elastomeric connectors made by suppliers such as PCK Elastomerics, Inc., Hatboro, Pa. and AT&T, Richmond, Va. Both the stacking connectors and the elastomeric connectors have the advantage that they can be positioned to connect areas anywhere on the circuit boards being connected and do not have to be located at the edges of the boards.
Once a decision has been made to use parallel circuit boards with interconnecting means between the boards, the connections on the boards must be configured so that the necessary circuits can be routed from the connecting areas to the proper destinations on the various boards. It is sometimes the case that some circuits can be "bussed" (connected in multiple) to adjacent boards, while others must be routed individually to specific boards. For example, in a semiconductor memory having individual memory chips arranged on parallel circuit boards, address, data and power circuits can be bussed to all the boards, but read and write circuits must be routed separately to each board. The kinds of connectors described above are all suitable for bussed connections as well as individually routed circuits, for example, as described in the final paragraph of the article referred to above.
It is desirable to minimize the number of different circuit board designs necessary when configuring a system using circuit boards stacked parallel to each other and even more desirable to be able to use the same design for each board in a stack. However, if it is necessary to route individual circuits to specific boards, as in the semiconductor memory described above, some arrangement must be devised by which such circuits can be routed from a source to a destination using identical boards. The invention to be described provides a solution to this problem.